25 votes
Accepted

Why is one meter as long as it is?

This number has no significance. Its origin is historical. Originally the meter was defined as 1/40,000,000 part of the Paris meridian. Based on the measurement of this meridian, they made a standard ...
Alexandre Eremenko's user avatar
14 votes

How did people count seconds before clocks were invented?

Electricity has nothing to do with the question. Clocks which could count minutes and seconds were purely mechanical and precise mechanical clocks (which could count seconds reliably) were invented in ...
Alexandre Eremenko's user avatar
9 votes
Accepted

How were negative numbers first used in physics?

Ancient Greeks painstakingly avoided negative numbers, although they could have come handy in astronomical calculations and number theory, among other places. Brahmagupta in Correctly Established ...
Conifold's user avatar
  • 75.2k
8 votes

Why is one meter as long as it is?

It's no more arbitrary than any other measurement unit, including the second. Nearly all modern values were chosed to try to avoid changing existing units' values while providing a source less ...
Carl Witthoft's user avatar
8 votes

What did the ratio of two magnitudes mean to ancient Greek mathematicians?

Fowler's Ratio in Early Greek Mathematics is a standard reference on the subject, see also his book Mathematics Of Plato's Academy (both are freely available). Book V, Definition 3 of Euclid's ...
Conifold's user avatar
  • 75.2k
7 votes
Accepted

How sensitive was the frog galvanoscope?

A frog galvanoscope does not measure voltage. Instead it detects electricity that same way that I detect my static charge after walking across a carpet in winter - by a short current flow. The current ...
David Bailey's user avatar
  • 1,222
6 votes
Accepted

Do astronomers still use decimal time?

Wikipedia refers to the Julian Date system, which is used, primarily by astronomers, to this day. It is convenient due to irregularities in the standard calendar periods. The Julian days give a ...
Conifold's user avatar
  • 75.2k
6 votes

How did people count seconds before clocks were invented?

How did people count seconds before clocks were invented? In general, they didn't, because there was no need to to so. The need for accuracy to the level of a second or less is a very recent need. ...
David Hammen's user avatar
  • 1,727
6 votes
Accepted

When was the measurement problem solved?

To a certain extend, the measurement problem (MP) is indeed philosophical, in the end, it still comes down to which interpretation you prefer. However, there are also of course also certain physical ...
Daniel's user avatar
  • 511
6 votes
Accepted

Why are revolutions per minute (RPM) still used instead of hertz (Hz)?

We often forget that even the minute is not an SI unit, only the second and its decimal multiples and fractions are. It is a leftover of the sexagesimal system (base 60), whose use predates the ...
Conifold's user avatar
  • 75.2k
6 votes

On the choice of Earth circumference vs diameter to define the meter

If one decides to choose some measurement of the Earth as a standard of length, circumference has one serious advantage: it is easier to measure directly. The Earth is not an exact sphere. And the ...
Alexandre Eremenko's user avatar
6 votes
Accepted

Ideas about the speed of light between Galileo and Romer?

I do not think it is a virtue to make unsupported assertions just because we happen to believe them now. Following available evidence does not makes one not smart or disappointing, that is how science ...
Conifold's user avatar
  • 75.2k
5 votes

When was the speed of a bullet or cannon ball first measured?

Some prehistory involving Aristotle, Tartaglia, Galileo and Torricelli can be found in The Impact of Ballistics on Mathematics by McMurran and Rickey. It was more speculative than experimental, and ...
Conifold's user avatar
  • 75.2k
5 votes
Accepted

First attempt to measure speeds using distance divided by time?

Greek astronomers of the Hellenistic epoch had a good understanding of time and speed in astronomy. They understood that neither Sun nor Moon move with constant speed, had the notion of average speed (...
Alexandre Eremenko's user avatar
4 votes
Accepted

History of cubit - Galilei, Kopernik, Newton

Issues regarding ancient measure systems are not easy to manage... Galileo Galilei, in Discorsi, uses braccia; the "old" translation by Crew & Di Salvio uses: "cubits". A braccio in Florence was:...
Mauro ALLEGRANZA's user avatar
4 votes
Accepted

Is it known where Eratosthenes first heard of the "well of Syene"?

The earliest extant description of Erathostenes' method is found in a book by Cleomedes written in the 1st century BC, and no wells are mentioned at all, if it's true that it's stated that whenever ...
xxavier's user avatar
  • 56
4 votes

Why is one meter as long as it is?

There's an important point that seems to have been missed here: it was initially proposed that the metre would be the length of a pendulum whose period would be equal to one second, when let swing at ...
Prime Mover's user avatar
  • 1,237
3 votes

Why does the US keep survey miles and feet?

Back in 1959, it was because the US had accumulated a lot of survey data using the older definition of the foot. For most people, the 2 PPM discrepancy between the two types of “foot” went unnoticed; ...
dan04's user avatar
  • 219
3 votes
Accepted

When and how did usage of the term Centigrade give way to Celsius? Are/were they in fact numerically identical?

The unabridged Oxford English dictionary clarifies the "when" part of the question. Also consult the paper in Nature (1949) https://www.nature.com/articles/163427a0 for the historic discussion (paper ...
AChem's user avatar
  • 4,049
3 votes

How did people measure electric charge at the time of Coulomb?

People did not. They generated and stored static electricity, but measuring it, other than by how strong the electic shock felt, was not yet done. Coulomb was the one who invented a way to do it in ...
Conifold's user avatar
  • 75.2k
3 votes

Wavelength definition of the metre

There are much easier ways to measure a wavelength than by "tromboning" an interferometer. A simple two-slit grating, for example, will give you a pretty decent measurement. You don't need to ...
Carl Witthoft's user avatar
3 votes

Who is the Westphal behind the Mohr-Westphal specific gravity balance? And how exactly did he improve on Mohr?

Quoth H. R. Jenemann, Die Geschichte der Dämpfung an der Laboratoriumswaage (1997, p. 240): In 1879, Georg Westphal filed a patent in Celle for a scale which was distinguished by various innovations ...
Francois Ziegler's user avatar
3 votes

Why does the statute mile have the length that it has?

The question is why 8 furlongs? Why forty poles, etc. Because furlongs and poles were already-standardized units that predated a c. 1300 measurement reform. These units couldn't be changed without ...
dan04's user avatar
  • 219
3 votes

First attempt to measure speeds using distance divided by time?

I'm not sure about Greeks, but Ossendrijver argues that Babylonian astronomers ca. 350-50 BCE used the trapezoidal rule to integrate Jupiter's motion along the ecliptic. The velocity is measured in ...
Michael E2's user avatar
  • 1,861
3 votes

First attempt to measure speeds using distance divided by time?

The Euclidean theory of proportion appears to speak against the ancient use of speed as a quotient between distance and time. Ratios, or proportions, according to that theory, were seen as legitimate ...
terry-s's user avatar
  • 4,375
3 votes

Did any "classical era" physicist foresee that a theory such as Quantum Mechanics is logically inescapable?

The following is far from "foreseeing" a "logical inescapability" of quantum mechanics, but I think it's quite interesting. Bernhard Riemann (not a physicist) is generally credited ...
Torsten Schoeneberg's user avatar
2 votes
Accepted

Lise Meitner's contribution to this experimental apparatus and research effort?

The above photo was reproduced in the biography: Lise Meitner, A life in Physics, by Ruth Lewin Sime; University Of California Press,1996, ISBN 0-520-20860-9. A brief description of the parts is given ...
Carmine D'Agosto's user avatar
2 votes

History of the word "scales" in graphing

There are (at least) three different English words written and pronounced “scale”. The “scale” of a fish or reptile is a borrowing from an Old French word adopted from a Germanic form cognate with ...
fdb's user avatar
  • 3,445
2 votes

What did the ratio of two magnitudes mean to ancient Greek mathematicians?

A small point, that I've only recently thought about: To my perception, most of classical-Greek mathematics had implicit units attached. Of "length" or "area" or "volume"....
paul garrett's user avatar
  • 1,006
2 votes

Wavelength definition of the metre

It was actually done with a "tromboning" Michelson Interferometer (https://www.bipm.org/en/measurement-units/history-si/former-prototype-metre.html) In 1892 by Michelson. He measured a distance ...
Martin Beckett's user avatar

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